1. Field of the Invention (Technical Field)
The present invention relates to electronic measurement and control, and more particularly to a method and apparatus to monitor the dispensing of caustic liquids or volatile liquid fuels and automatically terminate the dispensing process without human intervention in cases where the dispensing line leaks or breaks.
2. Background Art
In the delivery of hazardous liquids or volatile fuels a leak can occur in the delivery hose and the delivery personnel are unable or unwilling to control and shut down the system thereby causing environmental concerns and harm to life through fire, explosion, or other dangerous conditions.
Current methods employ a means to monitor the dispensing process for liquid propane gas, for example, by focusing on the pressure in the delivery system. Delivery trucks are typically equipped with constant velocity pumps that provide a constant flow of fuel to the destination tank under the drive pump mechanism. Many of these delivery systems are equipped with pressure sensors to detect a break or rupture of the delivery line. Such systems are unable to detect a leak until it has become so major that the pump can no longer maintain the pressure in the system at which time an alarm is triggered. The methods employed are mechanical in nature and are relatively inflexible and unintelligent. The means by which these systems operate focus on setting fixed points relative to known values in the dispensing process. Wide margins must be set to insure the system does not indicate falsely, thereby, allowing room for failures to go undetected. For example, a small hose leak would be indiscernible in a fixed point system. In some cases, the set points are fixed around a variable static pressure point. In this case, the pressure can vary but the relative trigger point is still fixed relative to the overall operation.
A typical pressure monitoring system typically works in the following manner. On arrival at a delivery location the operator either engages the power take off (PTO) from inside the vehicle or exits the vehicle and engages the PTO from the back of the vehicle. He proceeds to unroll the hose and take it to the tank where he checks the tank for current certification, makes the connection and returns to the back of the truck where he opens the main tank valve and increases the engine RPM to the proper delivery speed. He delivers a set amount per instructions or fills the tank to approximately eighty (80) percent. It is during this time that a leak may occur in the delivery system. The connection could come loose, the hose could rupture or a small leak could occur due to wear on the hose. The operator is then required to shut down the PTO, close the main tank valve and idle the engine. The time required to perform these tasks permits the loss of rapidly expanding volatile gas. On completion of the delivery the operator reduces the RPM, closes the main tank valve and disengages the PTO. The excess pressure is bled back in to the main tank and the operator removes the hose from the customer""s tank and returns it to the vehicle. If leak or break in the line occurs, the prior art systems rely on pressure sensors that monitor the liquid pressure and close valves when a predetermined pressure point is achieved.
U.S. Pat. Nos. 5,823,235 and 5,999,087 are two prior art methods that monitor the pressure and react to changes as described above.
Other prior art systems use mechanical hose plugs where the pressure drop will trigger the release of a plug to block the line.
Current systems are relatively inflexible in their implementation. The systems do not and cannot operate dynamically taking variable conditions under consideration. For instance, current methods do not cover low level leaks because pressure remains constant and the pressure switch trigger systems will not activate. In the flow of a liquid the pressure will remain relatively constant in the presence of a leak unless the line is completely severed. With a constant volume of fluid being pumped under pressure, the pressure drop would not be significant at the measuring point. The most common fail mode is a smaller rupture or hole where the flow will increase dramatically with a small decrease in pressure.
The present invention addresses the flow of the system and can detect the slightest leak and alarm the system long before the present prior art systems by monitoring the flow of the liquid. Even under conditions where the pressure begins to drop, this invention will arrest the leak if the flow rate increases.
Liquid Propane Gas expands exponentially when released into the atmosphere and being heavier than air collects in pockets where it is more likely to encounter fire, sparks, and other means of causing the gas to ignite with explosive force. Operators fear the result of a propane leak and may abandon a leaking vehicle instead of stopping the leak. Devices that must be attended by operators are fallible. This present invention, a self-monitoring system, is based on flow and pressure scientific data and the only operator functions are starting the sequence of events and ending the sequence after successfully delivering the load. In the event of over revving the engine by the operator, a warning is transmitted to the operator with a dwell time for the revolutions to be brought into pump manufacturers specs preventing damage to the vaned pump. Once delivery has started the system will shut down automatically in a few seconds after a leak is detected. This is a function of flow and pressure. This shut down interval is preset allowing the least amount of fuel to escape. The shut down sequence is complete and involves closing an electrically actuated inline ball valve and electronically interrupting the electrical flow to the vehicle""s coil shutting down the motor preventing back pressure build up on the pump and delivery system. A manual emergency shut down button is on the rear of the vehicle.
The current invention monitors flow rather than pressure to activate the shut-off mechanism. In the case where the delivery pump is a constant velocity type the system is limited in its ability to increase flow once set. If a leak were to occur with this type of pump, logic would suggest that the flow would not increase thereby making this invention inoperable. Contrary to this logic, in the pumping process the liquid or gas is under pressure from being pushed by the pump and restricted by the nozzle and the resistance of the walls of the conduit. When a leak occurs the escaping gas or liquid will flow through the hole as through the nozzle with pressure behind it. The hole must grow large enough to exceed the deliverable flow capacity point of the pump. The pump can maintain pressure under varying conditions but the flow will always increase.
The pressure of the main tank will vary throughout the day due to the temperature and depletion of its contents. Each time the system is activated to start a new delivery or transfer, new readings of pressure are taken for reference. Pressure is monitored to insure the system is ready to commence delivery and for the purpose of knowing if an overfill or kinked hose has occurred to stall the flow. A slowing of the flow is a natural operation at the end of a manual fill and is not used to trigger an alarm.
The preferred method for automatically shutting off a delivery system for a transfer of caustic or volatile liquids from a delivery container to a destination container when a leak occurs in the delivery system comprises determining if the liquid is pressurized in the delivery system, starting a flow of the liquid if the liquid is pressurized, monitoring a flow of the liquid, comparing the monitored flow of the liquid with a predetermined flow level, and terminating the flow of the liquid if the monitored flow exceeds the predetermined flow level. The method can also further comprise the step of performing initial systems checks and displaying delivery system status information. The preferred steps of starting a flow and terminating the flow comprise activating a valve. The preferred step of terminating the flow further comprises killing a liquid pump engine. The preferred step of comparing, further comprises delaying the comparing step for a predetermined amount of time. The method can also comprise logging delivery activities and downloading the logged delivery activities onto a computer. The method can also comprise the step of providing security mechanisms to avoid unauthorized access to the delivery system.
The preferred automatic shutoff apparatus for a delivery system when a leak occurs, the delivery system for transferring caustic or volatile liquids from a delivery container to a destination container, comprises a pressure sensor for verifying pressure in the delivery system, an apparatus to begin a flow of the liquid if the liquid is pressurized, a liquid flow monitor, structure for comparing an output of said liquid flow monitor with a predetermined flow level and an apparatus for terminating the flow of the liquid if said output exceeds the predetermined flow level. The preferred apparatus for beginning a flow and the apparatus for terminating a flow comprises a valve. The preferred valve further comprises an actuator. The preferred apparatus for terminating further comprises an engine kill apparatus. The automatic shutoff apparatus can also comprise a timer for delaying an activation of the structure for comparing. The automatic shutoff apparatus can also comprise an activity log. The activity log can also include a structure to download the activity log onto a computer. The activity log preferably comprises liquid pressure, liquid flow and liquid delivery amount. The activity log can also include a date of delivery, name of customer and address of customer. The invention can also comprise a security apparatus for preventing unauthorized use of the delivery system. The preferred security apparatus comprises a security code.
A primary object of the present invention is to provide a method and apparatus to immediately stop the flow of liquid upon the detection of a leak or rupture in the distribution system.
Another object of the present invention is to provide a means to automatically shut off the power train unit when a leak or rupture occurs in the distribution system.
Yet another object of the present invention is to provide a constant means for monitoring of liquid flow during delivery to detect possible leak in system.
Another object of the present invention is to provide a tally of total product pumped/delivered, incremental tally of individual delivery stops and a date and time stamp for every activity monitored.
Another object of the present invention is to provide a computer interface to a main computer to upload and download delivery and customer data.
Another object of the present invention is to provide automatic monitoring of system pressure and flow for automatically shutting down the system when the predefined amount of product is delivered or when the tank has reached a predetermined percentage total capacity.
A primary advantage of the present invention is that it monitors the flow rate of the liquid through the delivery system.
Another advantage of the present invention is that it is a self monitored system and an automatic system and requires no operator input.
Yet another advantage of the present invention is that it not only shuts off the flow during normal delivery of the delivered liquid, but also shuts off the flow when an inadvertent or accidental leak or rupture occurs.
Another advantage of the present invention is that the intelligent transducer converts a voltage input into relative flow and pressure data.
Other objects, advantages and novel features, and further scope of applicability of the present invention will be set forth in part in the detailed description to follow, taken in conjunction with the accompanying drawings, and in part will become apparent to those skilled in the art upon examination of the following, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.